"What? know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own? For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's" (1 Corinthians 6:19-20).
There are two reasons why we are not our own. (1) The Spirit has taken possession of us for God. (2) We are bought with a price, even the blood of Christ; it is a completed purchase. Purchased by blood, possessed by the Spirit, to be for God and His glory, our bodies are not our own to do as we will with them; we have no right to give them over to sin. The last words of the verse are not a cold, logical deduction from a previous argument, but an earnest exhortation suggested by the solemn thought of our oneness with Christ, and the price paid by Him to make us His.